1. Field of the Invention
This invention relates to the field of electronic powertrain controllers, and more particularly to the field of four-wheel drive vehicles which utilize an electronic powertrain controller.
2. Discussion of the Prior Art
Four-wheel drive vehicles provide traction often unattainable in two-wheel drive vehicles by delivering power to each of the vehicle's four wheels. Attendant with the added traction provided by four wheel drive is the added complexity of the drive train required to control and deliver power to all four wheels as opposed to only two wheels. For instance, it is desirable to alter the delivery of power to the front wheels and the rear wheels depending upon whether the vehicle is turning, or is being driven on low traction surfaces such as rain or ice covered surfaces to eliminate relative slip between the front and rear tires. Strategies designed to compensate for this slip must try to satisfy conflicting vehicle requirements, namely, the need to provide torque to a wheel pair and the need to release the limited slip device to prevent bindup. Rapid release of the limited slip device to prevent bindup may lead to an extended cycling condition, which in turn may produce NVH problems and durability concerns in the limited slip device.
The delivery of power between the front wheels and the rear wheels of the vehicle is typically handled by a transfer case mechanism, which includes either a mechanically or electronically controlled clutch. The inventors herein have recognized that known transfer case control systems experience problems particularly when turning on dry pavement where bindup is frequently experienced.
Accordingly, there is a need for a control mechanism for a transfer case in a four-wheel drive vehicle which balances the parameters of torque transfer between the front and rear wheels and release of the limited slip device, thereby preventing wheel bindup particularly during cornering on dry pavement.